An hypothesis under investigation in this laboratory is that gonococci are encapsulated in vivo and that multiple capsular serotypes induce serotype-specific immunity following infection. Capsules have been demonstrated in wet India ink preparations on four fresh isolates of gonococci during mid-logarithmic phase of growth in broth containing both proteose peptone and casein hydrolysate. Two strains examined in the electron microscope were surrounded by a structure external to the outer membrane of the cell wall which was made visible by antibody. This structure was not visualized with heterologous hyperimmune serum, suggesting that the two strains had antigenically distinct capsules. The capsule on N. gonorrhoeae will be examined to determine whether it has the same attributes as the meningococcal capsule. The number of antigenically distinct capsular types of gonococci will be determined with the Quellung reaction. Undegraded capsular antigens solubilized from organisms in mid-log phase will be characterized biochemically. Capsular antigens will be traced through purification with immunodiffusion using hyperimmune sera. Polysaccharide will be concentrated by precipitation with 80 percent ethanol and protein will be removed by solvent extractions. Capsular polysaccharide will be analyzed qualitatively, quantitatively and structurally. The function of the gonococcal capsule will be studied by examining the effect of anti-capsular serum on the morphologic interaction of organisms with human white cells adherent to glass coverslips. Hyperimmune rabbit sera generated by a single injection of live organisms will be expected to opsonize but not agglutinate the bacteria. The feasibility of producing a vaccine containing gonococcal capsular antigens can be assessed after the results of these investigations are available.